let R be the TRS under consideration

f(f(f(a,_1),_2),_3) -> f(f(_1,_3),f(_2,_3)) is in elim_R(R)
let r0 be the right-hand side of this rule
p0 = 0 is a position in r0
we have r0|p0 = f(_1,_3)
f(c,_4) -> _4 is in R
let l'0 be the left-hand side of this rule
theta0 = {_1/c, _3/_4} is a mgu of r0|p0 and l'0

==> f(f(f(a,c),_1),_2) -> f(_2,f(_1,_2)) is in EU_R^1
let r1 be the right-hand side of this rule
p1 = 1 is a position in r1
we have r1|p1 = f(_1,_2)
f(c,_3) -> _3 is in R
let l'1 be the left-hand side of this rule
theta1 = {_1/c, _2/_3} is a mgu of r1|p1 and l'1

==> f(f(f(a,c),c),_1) -> f(_1,_1) is in EU_R^2
let l be the left-hand side and r be the right-hand side of this rule
let p = epsilon
let theta = {_1/f(f(a,c),c)}
let theta' = {}
we have r|p = f(_1,_1) and
theta'(theta(l)) = theta(r|p)
so, theta(l) = f(f(f(a,c),c),f(f(a,c),c)) is non-terminating w.r.t. R

Termination disproved by the forward process
proof stopped at iteration i=2, depth k=3
11 rule(s) generated